S3 surging when running from cold

[beanoir]

I've noticed over the last few months recently that when driving the car from a cold start that it's not running as well as it should (or used to). There's a noise that sounds like the turbo keeps spinning up and down, and it feels like the engine is hunting a bit (if people still use that phrase!?). It's certainly not right but no idea to where to start, boost leak, actuator, MAF or something else? I'm not not much of an expert with FI on cars so don't know where to start.

It's booked in for a service in 2 weeks and to have top mounts done, so i'd like to try and figure out beforehand if possible, if not then i'll get the guys to sort it out when it's in.

Cheers

 

[Westy]

Is it a fluttering noise when boosting (not when letting off) that only occurs when cold/first few times on boost?

 

[beanoir]

No it's definitely not fluttering, it's a whirring noise almost like a fan...it's also not very responsive on the accelerator when this is happening. After about 5 minutes it pretty much dissapears.

 

[Westy]

No it's definitely not fluttering, it's a whirring noise almost like a fan...

That's good then cause my fluttering turned out to be a seriously cracked turbo housing. What engine code have you got? SAI?

 

[beanoir]

Its an AMK.

I could do without it being a shot turbo, which to be fair would surprise me as it's still low mileage and not hard a hard life, but I know it still happens.

 

[Westy]

Its an AMK.

I could do without it being a shot turbo, which to be fair would surprise me as it's still low mileage and not hard a hard life, but I know it still happens.

Does it make the noise on idle? Can you get your head in the engine bay and pinpoint the noise? Only way to fully know if it's the turbo will be to get it stripped and refurbed.

 

[beanoir]

No, no noise at all on idle...whihc thinking about it that tells me something doesn't it...?

 

[Westy]

No, no noise at all on idle...whihc thinking about it that tells me something doesn't it...?

What about if you rev the engine at a standstill? The PAS pump can whine at revs if the fluid is low.

 

[beanoir]

I'll have a check in the morning and see if it does Westy, the fluid level in the PAS is all good. Cheers fella!

 

[beanoir]

Turns out I had a faulty N75 valve, it's not only cured the problem I had with the surging but the boost now holds much better and more consistently through the revs....great little fix that one!

 

[Sam_]

Mine's doing similar but I fitted a new OEM N75 about 6 months back. Might try another one?

 

[beanoir]

i think you can perform a test to decide if the N75 is shot, unplugging it maybe? Or i'm sure VCDS will tell you also.

 

[IrishDave]

I am having a similar problem. How much are N75 valves.